1. Field of the Invention
The present invention relates to a method of molding a socket for a joint by expanding the edge of a plastic resin tube.
2. Description of the Prior Art
When a plastic resin tube, especially a rigid polyvinyl chloride tube is jointed, the edge of the resin tube has been expanded by using a mold so as to form socket.
The shapes of the socket have been the socket S having slight tapered inner surface as shown in FIG. 8(a). (hereinafter referring to as a TS socket); a socket having annular groove G in circumferencial direction so as to fit the annular packing as shown in FIG. 8(b) (hereinafter referring to as RR socket).
The thickness t.sub.2 of the socket or the thickness t.sub.3 of the groove G become smaller than the thickness t.sub.1 of the resin tube P whereby the pressure resistance and impact strength of the part are disadvantageously lowered.
It has been known that the thickness of the socket is increased by pushing the edge of the resin tube to the axial direction when the socket is molded by expanding the diameter of the edge of the resin tube. However, in the conventional method, the resin tube is pushed between the male mold for expanding the diameter which has the outer diameter larger than the inner diameter of the resin tube P, and the female mold surrounding the tube with the space larger than the thickness t.sub.1 of the tube, whereby the thickness increasing work and the diameter expanding work are simultaneously carried out. Accordingly the male mold and the female mold should be taken out to different direction after molding the socket.
Accordingly, the removal of the female mold has not been easy depending upon the length of the resin tube. Moreover, the movements of the resin tube and the molds are complicated whereby the continuous molding operation could not be attained.